ScienceAges 13-15

Acids, bases & the pH scale

Use the 0–14 pH scale, indicators and neutralisation reactions to classify acidic, neutral and alkaline solutions. Review suitability for your learners before teaching.

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Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
2. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
5. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
6. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
7. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
8. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
9. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
10. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
11. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
12. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

12 questions · Seed 50 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
A strong acid fully ionises (dissociates), whereas a weak acid only partially ionises
Acid strength refers to the degree of ionisation in water.
2. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
Ethanoic (acetic) acid
Vinegar is a dilute aqueous solution of ethanoic (acetic) acid.
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
Green
Universal Indicator is green at neutral pH 7, red in strong acid, and purple in strong alkali.
4. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?
Colourless in acid and pink in alkali
Phenolphthalein is colourless below pH 8.2 and turns pink-magenta in alkaline solutions.
5. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
6. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?
Hydrogen
Metal + Acid → Salt + Hydrogen gas (which gives a squeaky pop with a lighted splint).
7. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
A salt and water
Acid + Alkali → Salt + Water (H⁺ + OH⁻ → H₂O).
8. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?
Burette
A burette delivers variable volumes accurately to within 0.05 cm³.
9. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
Blue
Alkalis turn red litmus paper blue.
10. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
It turns clear limewater cloudy (milky)
CO₂ reacts with calcium hydroxide (limewater) to form an insoluble white precipitate of calcium carbonate.
11. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
Carbon dioxide
Acid + Carbonate → Salt + Water + Carbon dioxide (which turns limewater milky).
12. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
10
pH = −log₁₀[H⁺], so each whole unit decrease represents a tenfold increase in [H⁺].

12 questions · Seed 50 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 13-15

Acids, bases & the pH scale

Take your time. Show your thinking.

1. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
2. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
4. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
5. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
6. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
7. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
8. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
9. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
10. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
11. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution
12. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
pH Scale: 0 (Acid) → 7 → 14 (Alkali) · Indicator Solution

12 questions · Seed 50 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 13-15

Acids, bases & the pH scale

Answers and reasoning. Review before teaching.

1. What is the difference between a strong acid (like HCl) and a weak acid (like ethanoic acid) in water: a strong acid fully ionises (dissociates), whereas a weak acid only partially ionises, or a strong acid has pH 12?
A strong acid fully ionises (dissociates), whereas a weak acid only partially ionises
Acid strength refers to the degree of ionisation in water.
2. What weak organic acid gives vinegar its sour taste: ethanoic (acetic) acid or nitric acid?
Ethanoic (acetic) acid
Vinegar is a dilute aqueous solution of ethanoic (acetic) acid.
3. What colour does Universal Indicator turn in a neutral solution of pH 7: green or red?
Green
Universal Indicator is green at neutral pH 7, red in strong acid, and purple in strong alkali.
4. What colour is phenolphthalein indicator in an acidic solution vs a basic solution: colourless in acid and pink in alkali, or blue in both?
Colourless in acid and pink in alkali
Phenolphthalein is colourless below pH 8.2 and turns pink-magenta in alkaline solutions.
5. What colour does blue litmus paper turn when dipped into an acidic solution: red or blue?
Red
Acids turn blue litmus paper red.
6. Which gas is produced when a reactive metal (such as magnesium or zinc) reacts with dilute hydrochloric acid: hydrogen or oxygen?
Hydrogen
Metal + Acid → Salt + Hydrogen gas (which gives a squeaky pop with a lighted splint).
7. What are the two products formed when an acid reacts with an alkali in a neutralisation reaction: a salt and water, or hydrogen and carbon?
A salt and water
Acid + Alkali → Salt + Water (H⁺ + OH⁻ → H₂O).
8. In an acid–base titration, which piece of graduated glassware with a tap at the bottom is used to measure the exact volume of acid or alkali added: a burette or a beaker?
Burette
A burette delivers variable volumes accurately to within 0.05 cm³.
9. What colour does red litmus paper turn when dipped into an alkaline solution: blue or yellow?
Blue
Alkalis turn red litmus paper blue.
10. What is the chemical test that confirms a gas is carbon dioxide (CO₂): it turns clear limewater cloudy (milky), or it relights a glowing splint?
It turns clear limewater cloudy (milky)
CO₂ reacts with calcium hydroxide (limewater) to form an insoluble white precipitate of calcium carbonate.
11. Which gas is produced when a metal carbonate (such as calcium carbonate) reacts with an acid: carbon dioxide or nitrogen?
Carbon dioxide
Acid + Carbonate → Salt + Water + Carbon dioxide (which turns limewater milky).
12. Because the pH scale is logarithmic, a decrease of 1 pH unit (e.g. from pH 4 to pH 3) means the H⁺ ion concentration increases by a factor of: 10 or 2?
10
pH = −log₁₀[H⁺], so each whole unit decrease represents a tenfold increase in [H⁺].

12 questions · Seed 50 · Age guidance, not curriculum certification